What happened to my Python file?

Question

I've been working on creating a ray caster in Python, using Pygame, and I went back to work on it earlier today to find that it would not load properly. When I opened it, it appeared as if it were a new python document. I then tried to run it to see if that would make a difference, and it gave me the error:

I have an older version of the file saved in the same directory too, and you can see that the apparently empty file still is a larger size than the one that still works. This suggests to me that the data is there, I just can't access it.

Is there a way to recover the data at all, and what can I do to stop this in the future?

EDIT:

This is a screenshot showing what the file looks like once opened